Political and sporting heavyweights have been lobbying in Singapore on Monday as the race to host the 2012 Olympics intensifies.
England football captain David Beckham flew in to join Prime Minister Tony Blair in supporting London ahead of Wednesday's decision - due at 1246 BST.
And boxing legend Muhammad Ali is due to make an appearance to back New York.
Paris is regarded as favourite to win the vote, with Madrid and Moscow also competing for hosting rights.
Beckham and his wife Victoria slipped quietly through the VIP reception area of Changi Airport before heading to a reception hosted by the British High Commissioner.
There, Mr Blair hailed the capital's "brilliant" bid to host the Games and said the event would provide a "wonderful legacy" for British sport.
The Prime Minister also moved to play down the rivalry between Paris and London.
A row broke out earlier on Monday when Paris' Stade de France stadium, the centrepiece for its bid, was criticised at a London 2012 news briefing.
Paris did not lodge an official complaint and International Olympic Committee president Jacques Rogge later said the comments did not contravene rules.
Mr Blair said: "It's not about the rivalry between France and the UK. All these cities are big powerful cities with good bids."
Beckham wore a dark three-piece suit despite the tropical humidity, with his wife opting for an indigo cocktail dress and snake-skin style stilettos.
The England captain said: "We are backing the bid because we believe in it.
"Obviously it's going to generate a lot of things for our country. I believe this is the only place it should be."
The Princess Royal was also at the reception along with many of London's bid ambassadors, including Olympic rowing great Sir Steve Redgrave, Paralympian Tanni-Grey Thompson and football hero Sir Bobby Charlton.
The prime minister will spend a hectic 48 hours in Singapore lobbying IOC members before flying back to the UK before the vote, to host the G8 summit at Gleneagles in Scotland.
French president Jacques Chirac is due to arrive in Singapore on Tuesday to lobby for Paris.
The French capital's bid team were upset when at a London news conference, Sydney 2000 organising chief Jim Sloman and architect Rod Sheard suggested the Stade de France was not ideally suited to stage Olympic athletic events.
However, Rogge later cleared London of breaching strict regulations regarding the criticism of rival cities.
In another development, British Olympic Association chief Craig Reedie denied a voting deal has been done with Madrid.
It had been reported that London wants to secure the Spanish capital's votes should they be knocked out of Wednesday's vote.
Beckham's Real Madrid team-mate Raul was among the Spanish delegation led by Queen Sofia.
Bid president Feliciano Mayoral believes Madrid has done everything in its power to secure the Games.
"We have not made any errors and have presented an excellent candidacy to organise the Games," he said.
Meanwhile, New York bid leaders held an upbeat news conference at which they pledged to win the vote as a birthday present for President George Bush, who turns 59 on Wednesday.
The New York bid looked to be on the rocks after problems securing a site for a stadium, but last month they submitted plans for a new stadium in Queens.
Mayor Michael Bloomberg said: "We're going to win this one. The momentum we have generated is really coming together at exactly the right time.
"You saw us like an athlete who fell and got back up and said 'OK, just a little more of a challenge' and went out and ran even harder."
Moscow mayor Yuri Luzhkov arrived in Singapore in confident mood, despite the Russian capital's outsider status.
"We are optimistic about our chances for one simple reason," he said.
"We are sure members of the IOC will come to the conclusion that only one city will be fundamentally changed by hosting the Games.
"The choice of Moscow is similar to that of Beijing for 2008. It will be historic."
The opening ceremony for the 117th IOC session takes place on Tuesday.
Rogge has suggested that Wednesday's final outcome could be decided by as few as half a dozen votes.
Each country will make a 45-minute presentation on Wednesday, before an evaluation commission report, the final vote and then the all-important announcement.
Tuesday: 117th IOC Session opening ceremony, Moscow news conference
Wednesday: Bid presentations; evaluation committee report; vote; announcement
Each of the cities is wheeling out its most famous sporting names to promote their bids.
Laurent Blanc, Michel Jazy and Marie-Jose Perec are turning out for Paris.
Moscow has swimmer Alexander Popov while Ali will weigh in for New York.
But the icons are forbidden by IOC rules from making public appearances.
The most important figures are the members of the bid teams, who have spent two years putting together their bids.
They will hone their bids and lobby members of the IOC committee before making final presentations.